Old English rife "abundant, common, prevalent," from Proto-Germanic *rif- (cf. Old Norse rifr, Swedish river, Norwegian riv, Middle Dutch riif, Middle Low German rive "abundant, generous"), said to be from PIE root *rei- "to scratch, tear, cut" "The prevalence of the word in early southern texts is in favour of its being native in English, rather than an adoption from Scandinavian." [OED]